Heat exchanger



y 1948- F. R. HANRAHAN 2,445,115

HEAT Exc'nmem Filed April 7, 1944 2 Sheets-Sheet 2 FIG?) gwoenkw Patented July 13, 1948 HEAT EXCHANGEB Francis -P. Hanrahan, Washington, D. 0., assignor to United States of America a represented by the Secretary of Agriculture Application April 7, 1944, Serial No. 529,970

2 Claims. 257-246) (Granted under the act of March 8, 1883, as amended April 30, 1928; 370 0. G. 757) This application is made under the act of March 3, 1883', as amended by the act of April 30, 1928, and the invention herein described and claimed, if patented, may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment to me of any royalty there- This invention relates to apparatus for the rapid or flash exchange or transfer of heat in the treatment of fluids, such as milk and other foods. crude oil, and so forth.

The principal object of this invention is the provision of an apparatus of the type mentioned in which the fluid is rapidly heated or cooled while it flows continuously through the apparatus for such purposes as sterilization, pasteurization, forewarming, preheating under pressure for the purpose of spray drying, flash cooling, and so forth. Another object of this invention is the provision of an apparatus of the type mentioned which will not materially change the flavor of foods which may be processed therein Devices of the prior art designed to accomplish treatments of this kind have the disadvantage of being difllcult to disassemble and hence are difficult to clean. Others are more or less complicated in structure, occupy large spaces, and are not satisfactory with respect to sanitation. This invention overcomes many of these difliculties. It is simple and compact in structure and design, can be easily disassembled and cleaned, and can be used to meet high sanitation requirements.

In general, this invention comprises a longitudinal housing containing a removable helical screw through which the fluid to be treated flows continuously. Heat is applied through the walls of the housing and also through the screw by suitable means. Various forms of helical screws may be used.

The following description, considered together with the accompanying drawing, will more fully disclose this invention and further objects and advantages thereof will be apparent.

In the drawing:

Figure 1 is a longitudinal section of an embodiment of this invention with a part of the screw shown in elevation.

Figure 2 is a view similar to Figure 1 of another embodiment in which the screw is conical.

Figure 3 is a similar view of a third embodiment in which means are provided for the injection of conditioning fluids, such as steam, into the material being treated.

or the drawing, the embodiment illustrated comprises a tubular housing ll having an inlet l2 and an outlet l3 (interchangeable). Within the housing, there is disposed a helical screw l4 carried by a hollow shaft l 5; the helical screw forms a continuous groove l6 between the inlet l2 and the outlet I3. The outer extremities of the screw I! contact the inner surfaces of the housing ll, whereby the groove 16 becomes a completely confined space between the ends thereof.

It is preferable to have the helical screw of a material having a coeiiicient of expansion different from that of the housing II. If the apparatus is to be used for heating purposes, the coeflicient of expansion should be greater; if for cooling purposes, it should be less so that during operation, the change in temperature will cause the screw to become wedged tight against the inner surface of the housing and prevent leakage therebetween.

The shaft I5 is provided near each of its ends with a collar ll adjacent the outer side of which packing material i8 is disposed and a packing gland IS. The housing I I is provided with means around the area adjacent the screw l5 for heating or cooling the material to be treated. Such means may be either mechanical or electrical. The embodiment illustrated employs a jacket 20 having an outlet 2i andan inlet 22 for steam, hot water, or other fluids.

In operation, the fluid to be treated is introduced into the apparatus under pressure through the outlet l2 from whence it flows through the helical groove l6, leaving the apparatus through the outlet I3. Steam, for example, is applied to the jacket 20 and also through the hollow core of the shaft l5. Heat is radially conducted very rapidly through the walls of the housing and shaft while the threads of the screw l5 conduct heat axially. Consequently, the material being treated is acted upon in four directions and since the cross-sectional area of the material is very small while flowing through the groove of the screw and further since the heat is applied in a cross-sectional direction, it is apparent that very rapid heating or cooling can be accomplished with the apparatus.

To clean the apparatus, it is only necessary to remove the packing glands IS. The screw is then immediately accessible to washing and brushing,

, and the interior of the housing is easily flushed ing 23 and screw 24 are conically shaped, substantially as shown. This arrangement obviates the necessity forusing materials of different coefficients of expansion for the housing and screw in order to obtain a tight flt, since the larger packing gland 25 can be used to exert an axial thrust toward the smaller end and thereby push the screw solidly against the inner surface of the housing. At the smaller end of the shaft, packing material 26 is disposed between a gland 21 and a flanged portion 28 of the housing so that pressure applied by the gland 21 will not exert a force against the shaft opposite to that of the large gland 25 since to do so would tend to displace the screw from contact with the housing 23.

The embodiment illustrated in Figure 3 com-' prises a tubular housing 29 containing a helical screw 30 carried by a shaft 3| similar to that of Figure 1, except that one end 32 of the shaft is sealed and small apertures 33 are radially disposed on the shaft between the turns of the screw. The other end of the shaft is provided with a flange 34 and packing material 35 is disposed between the flange and an annular shoulder 36 of the housing 29. The gland 31 is disposed against the outer face of the flange 34 substantially as illustrated. The inlet for the introduction of the fluid to be treated is designated by the numeral 38 while the outlet 39 may be axially disposed as shown in the drawing. In this embodiment, a conditioning fluid, such as steam, may be forced into tubular shaft 3| and injected into the material being treated through the apertures 33.

It is to be understood that although only single thread screws have been shown in the drawing, multiple thread screws may be employed in order to increase capacity.

In using apparatus of this general type for the heating of milk, difficulty has heretofore been encountered due to the tendency of constituents of the milk to stick to the apparatus. When this condition exists, it is necessary for the pressure to be increased in order to force the milk through the apparatus and in most instances this pressure must be very high Also the material sticking to the apparatus acts to insulate the milk from the heating medium. Both f these effects operate to decrease eihciency andwaste materials. One method of overcoming this difficulty is to create turbulence in the stream of fluid being treated. If the force exerted by the turbulence is greater than the adhesive force between the constituents and the surface of the apparatus over which they flow, there will naturally be a tendency for the sticking condition to be avoided. The greater the turbulence the less material is likely to stick on the apparatus. It is'well known that turbulence is created when the fluid stream is caused to change direction. The greater the change of direction and the more frequently the change occurs, the more turbulence will be cre- ,ated. In this connection, the optimum condition relative to the frequency factor resides in the use of circular coils because such coils would result in the continuous change of direction of the fluid. The degree of change, however, depends upon the diameter of the coil and is inversely proportional to it. In other Words, it is desirable to use circular coils having the smallest practical diameter. Although this principle is known and utilized in prior devices that employ coils of tubular materials, there is a limit to the diameter to which such coils may be restricted, since this diameter depends not only upon the wall thickness of the coils, but also upon the diameter of the tubes, Tube diameter is a liniiting factor because if too small, the pressure necessary to force the material through the tube would be prohibitive. However, with the present invention. the diameter of the screws can be made as small as desired without being limited by the factors involved in the ordinary tubular coils.

Having thus described my invention, I claim:

1. A heat exchanger comprising a. conical outer shell through the walls of which heat exchange is effected, a jacket for holding a heat exchange fluid against the exterior of the shell, a removable conical inner shell within said outer shell adapted to carry a heat exchange fluid through its center and having a spiral channel at its outer surface adapted to carry a fluid in contact with the inner surface of the outer shell, the ends of said channel being at opposite ends of said inner shell, means for introducing a fluid into one end of said channel, means for withdrawing fluid from the other end of the channel, a packing gland at the smaller end of and siidably engaged with the outer shell, means for adiustably securing said packing gland in different positions on said inner shell, another packing gland at the other end of and slidably engaged with the inner shell, and means for adjustably securing said last-mentioned gland in different positions on said outer shell.

2. A heat exchanger adapted to high standards of sanitation and efficiency comprising a housing having a tapered interior, a fluid Jacket on the exterior of the housing having means for introducing and removing fluids therefrom, a removable inner shell having a tapered exterior provided with a fluid-conducting spiral channel, said inner shell being adapted to contact fit the interior surface of the housing, two co-acting screw packing glands, one being adapted to an externally threaded cylindrical extension of the smaller end of the removable inner shell and the other gland being adapted to an internally threaded cylindrical extension of the larger end of the tapered interior of the housing, means for introducing and withdrawing fluid from the said channel, and independent means for introducing and removing conditioning fluid from the core of the inner shell.

FRANCIS P. HANRAHAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 536,354 Kohl Mar. 26, 1895 1,046,298 Hurley Dec. 3, 1912 1,657,202 Ellyson Jan. 24, 1928 1,815,938 Trogner July 28, 1931 1,854,619 Mortensen Apr. 19, 1932 2,003,593 Jacobsen June 4, 1935 2,053,623 McKerrall Sept. 8, 1936 2,066,480 McKerrall Jan. 5, 1937 

